EP0063619B1 - Verfahren und Vorrichtung zum Impulslichtbogenschweissen - Google Patents

Verfahren und Vorrichtung zum Impulslichtbogenschweissen Download PDF

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Publication number
EP0063619B1
EP0063619B1 EP81103065A EP81103065A EP0063619B1 EP 0063619 B1 EP0063619 B1 EP 0063619B1 EP 81103065 A EP81103065 A EP 81103065A EP 81103065 A EP81103065 A EP 81103065A EP 0063619 B1 EP0063619 B1 EP 0063619B1
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EP
European Patent Office
Prior art keywords
current
pulse
welding
background
detecting
Prior art date
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Expired
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EP81103065A
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English (en)
French (fr)
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EP0063619A1 (de
Inventor
Hideyuki Yamamoto
Waichi Nishikawa
Moritoshi Nagasaka
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Daihen Corp
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Osaka Transformer Co Ltd
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Priority to EP81103065A priority Critical patent/EP0063619B1/de
Priority to DE8181103065T priority patent/DE3173176D1/de
Publication of EP0063619A1 publication Critical patent/EP0063619A1/de
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Publication of EP0063619B1 publication Critical patent/EP0063619B1/de
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/09—Arrangements or circuits for arc welding with pulsed current or voltage
    • B23K9/091—Arrangements or circuits for arc welding with pulsed current or voltage characterised by the circuits

Definitions

  • the present invention relates to a pulse arc welding method and device, in which a consumable electrode is supplied at a constant speed.
  • a consumable electrode fed at a constant speed has its forward end portion facing a workpiece being fused and separated to produce droplets (small size drops) which are transferred to the workpiece in a manner of spray transfer.
  • the consumable electrode is supplied with a low level background current below a critical current level capable of spray transporting and a train of pulse current imposed on the background current and having a level above the critical current level. The spray transfer of the consumable electrode is carried out only when the pulse is applied.
  • the power supplying device includes a background current supplying source (hereinafter referred to as a background source) and a pulse current supplying source (hereinafter referred to as a pulse source) in which either one of the background source and pulse source has a constant voltage characteristic.
  • a background current supplying source hereinafter referred to as a background source
  • a pulse current supplying source hereinafter referred to as a pulse source
  • the pulse arc welder according to the prior art for carrying out the welding with a constant wire- feed system is either of a first type in which the background source has a constant voltage characteristic and the pulse source has a constant current characteristic, or drooping characteristic, with a small inclination, or a second type in which the background source has a constant current characteristic and the pulse source has a constant voltage characteristic.
  • first and second types are shown in the graphs of Figs. 2 and 3, respectively, relatively with arc characteristic.
  • abscissa and ordinate represent current I and voltage V, respectively
  • a real line B-CP indicates the constant voltage characteristic of the background source
  • a dotted curve P-CC indicates the constant current characteristic (drooping characteristic) of the pulse source.
  • chain lines L0, L1 and L2 indicate arc characteristic of different arc length.
  • the graph of Fig. 2 represents the above described first type arc welder which has, as understood from the graph, such an advantageous feature that spray transfer can be carried out stably because the pulse current level Ip is maintained stable regardless of change of arc length, e.g., from L0 to L1, or to L2, caused by irregular surface of the workpiece or unexpected shaking of the arc welder.
  • the fluctuation in the arc length adversely affects the arc voltage average value Va such that, as the arc length becomes longer, e.g., from L2 to L0 and further to L1, the acting point on the line B-CP shifts towards lower region of the current I, and therefore, the arc voltage average value Va gradually increases from Va2 to Va1, that is, to a region accessible to no-load voltage Vbo, resulting in unstableness of the arc.
  • Such an unstableness is particularly serious when the arc welder is adjusted with low background current level to produce low no-load voltage Vbo.
  • the graph of Fig. 3 represents the above described second type arc welder which has, as understood from the graph, such an advantage that the welding arc is maintained stable regardless of fluctuation of arc length even if the background current level is fixed to a considerably low level since the background source has the drooping characteristic.
  • the pulse current level greatly changes with respect to the flucutation of the arc length, e.g., from LO to L1, or to L2, resulting in change in the size of the molten drops released from the electrode.
  • Such a change in the size often results, in, particularly when the pulse current level is reduced, a globular (large size drop) transfer of fused electrode that intercepts the smooth welding process of spray transfer.
  • the arc welding method according to the present invention allows to carry out the smooth welding of spray transfer regardless of fluctuation in the arc length and to produce a stable constant arc from the consumable electrode which is being fed at a constant speed.
  • the arc welding method comprises the steps of unifying the pulse current level to a predetermined level, setting the background source with the constant current characteristic, and comparing the detected arc voltage level with a predetermined level, thereby maintaining the arc voltage constant by changing arc length.
  • a pulse arc welding device for welding a workpiece by an arc produced between a consumable electrode which is fed towards the workpiece at a constant speed and the workpiece comprising, means for generating a background current, means for generating a pulse current, means for imposing the pulse current on the background current, means for detecting the welding voltage measured between the consumable electrode and the workpiece for producing a welding voltage signal, means for producing a reference signal indicative of a desired welding voltage, and means for comparing the welding voltage signal with the reference signal for producing a difference signal indicative of the difference therebetween.
  • the factors in the pulse current that influences the continuous spray transfer are pulse current level lp, pulse duration Tp and pulse frequency f. Although these three factors influence, together with the background current, degree of heating and fusion of the forwarding end portion of the consumable electrode, the most important factor for separating the fused electrode is the pulse current level Ip which produces a force proportional to Ip 2 by a so-called pinch effect. Therefore, when the pulse current level Ip increases to a high level, the fused electrode can be separated into droplets (very small particles) which are spray transferred constantly to the workpiece, thus carrying out an optimum welding process.
  • the pulse current level Ip decreases to a low level
  • the fused electrode is separated by globulars (large drops) which are intermittently deposited along the workpiece. Therefore, it is necessary to prevent the pulse current level Ip from being dropped below a predetermined level, and preferably the pulse current level Ip should be maintained at a desired level.
  • the separation of the fused electrode is controlled by the pinch force effected by the pulse current level lp, the separation of the fused electrode is also relative to the pulse duration Tp. Therefore, the condition in which the fused electrode is separated is determined by the pulse current level Ip and pulse duration Tp, and examples of such a condition are shown in graph of Fig. 4 in which abscissa and ordinate represent pulse duration Tp (ms) and pulse current level lp(A).
  • a curve indicated by a numeral 1.6D shows a border line of a region in which the spray transfer can be carried out using 1.6 mm diameter stainless steel as the consumable electrode in 2% 0 2 +Ar inert-gas.
  • the pulse arc welding with spray transfer can be carried out in a region above the curve 1.6D.
  • curves 1.2D and 0.8D show border lines of such a region using 1.2 mm diameter stainless steel and 0.8 mm diameter stainless steel, respectively, as the consumable electrode in 2% 0 2 +Ar inert-gas.
  • Dotted lines 1.61, 1.21 and 0.81 show critical current level for the stainless steel consumable electrodes of 1.6 mm, 1.2 mm and 0.8 mm diameters, respectively. These critical current levels show the minimum available average welding current level for carrying out the spray transfer.
  • Tp in order to proceed the spray transfer with a short pulse duration, for example, 5 ms or less, Ip2.
  • Tp must have a certain value determined by the diameter of the consumable electrode.
  • the condition in which the spray transfer can be carried out is determined both by the parameters Tb and lp, but in the region with long pulse duration Tp, such a condition is determined solely by the pulse current level lp.
  • the parameter of the pulse duration Tp affects, together with the parameter of background current, the heating and fusion of the end of the consumable electrode.
  • the transfer of the fused electrode is carried out during the supply of pulse current, such a transfer will not be carried out properly unless the end of the consumable electrode is heated and fused.
  • the increase of the pulse frequency f does not necessarily mean that such an increase directly expedites the transfer of the fused electrode. Therefore, it can be said that the pulse frequency f will not directly effect the separation of the fused electrode, as in a manner effected by the above described value lp 2 Tp.
  • the pulse current level Ip which controls the separation of the fused electrode. Therefore, it is necessary to maintain the pulse current levellp approximately equal to a predetermined level.
  • the welding current average value la is determined by the parameters of background current level Ib, background current period Tb, pulse current level Ip and pulse duration Tp, the pulse current level Ip must be maintained to a predetermined level as explained above, and therefore, it can not be varied for the control of .the welding current average value la. Furthermore, since the background current period Tb is determined by the period (T-Tp), it can not be varied independently.
  • the background source employing a feedback circuit to make it operable with constant current characteristic, and accordingly producing a constant background current Ib, has such advantages that its conatrol is very simple and it does not require any additional power source for its control, and from this point of view, the rearrangement of the background source to allow the change in background current level lb can be realized only when these advantages are deserted.
  • the pulse duration Tp this can be used to control the welding current average value la with a limitation that the pulse duration Tp is not in the region in which the pulse duration Tp affects the determination of border line of the spray transfer described above in connection with Fig. 4, i.e., with a limitation that the pulse duration Tp is greater than, according to the example of Fig. 4, about 6 ms. Accordingly, it can be concluded that the parameters which can be used for controlling the welding current average value la are one cycle period T which can be evaluated by pulse frequency f and is the most convenient parameter, pulse duration Tp which comes next, and background current level lb.
  • a graph depicted therein shows output characteristics of the background source and pulse source and arc characteristic of a pulse arc welding device according to the present invention.
  • abscissa and ordinate represent, respectively, current and voltage
  • a dotted line P-CC indicates constant current characteristic of the pulse source and is similar to that shown in Fig. 2.
  • This constant current characteristic can be obtained by the use of a feedback circuit which controls the pulse current level Ip by a signal indicative of a difference between a predetermined reference level and the feedback pulse current level lp, or its average value lpa.
  • the background source As to the background source, it is necessary to set the no-load voltage of the background source to a considerably high level to prevent the arc from being produced intermittently, and for this purpose, the background source has a constant current characteristic as shown in Fig. 5 by a real line B-CC.
  • the background source when the background source is arranged to have constant current characteristic, the self-regulating effect of the arc by the source becomes less effective, and accordingly, it is necessary to provide a means to detect the arc length and to control the arc length approximately equal to a predetermined length.
  • the control of the arc length can be carried out by the control of fusing speed of the constantly fed consumable electrode, and such a fusing speed can be controlled by the change of the welding current average value. The manner in which the arc length is controlled is described in detail below.
  • a voltage drop between the consumable electrode and the workpiece hereinafter referred to as an arc voltage level
  • a reference voltage a voltage drop between the consumable electrode and the workpiece
  • the welding current average value la is decreased by the decrease of any one or in combination of the parameters of pulse frequency f, pulse duration Tp and background current level lb.
  • the decrease of welding current average value la results in decrease of the arc length, and as a consequence, the arc length is again set to the desired length.
  • a similar procedure is taken when the arc voltage level becomes smaller than the reference voltage.
  • the above described arc voltage level can be detected relatively by the background voltage average value Vba or arc voltage average value Va.
  • the arc voltage level should preferably be detected relatively by the pulse voltage average value Vpa for allowing more precise detection than when the above value Vba or Va is used.
  • the arc voltage can be detected relatively by the background voltage level Vb sampled during the background current period Tb, or by the pulse voltage level Vp sampled during the pulse duration Tp.
  • the pulse current level lp can be maintained approximately equal to a predetermined level, the separation of the fused electrode can be carried out uniformly, and at the same time, the weld penetration can be effected with uniform depth, and therefore, a desirable penetration welding can be carried out. Furthermore, since the background source has a constant current, or drooping, characteristic, arc will not be intercepted even if the background current level is fixed to a low level, and therefore, stable arc can be maintained during the operation.
  • the above described method according to the present invention can be applied to low current welder for welding thin plates or to high speed welder without producing spatters such as short-circuiting transfer.
  • a pulse arc welding device according to the first embodiment of the present invention.
  • the welding device of the first embodiment is so arranged as to control the arc voltage, which is approximately proportional to the arc length and thus arc length, constant by way of control of the pulse frequency.
  • the welding device shown comprises a source of DC power, a background current generator, a pulse current generator, a consumable electrode feeding control and a welding power control which is, according to the first embodiment, formed by a pulse frequency control.
  • the source of DC power includes a three-phase transformer WT for receiving three-phase AC power, a group of rectifiers SR1 coupled to the three-phase transformer WT and a capacitor 3 connected between lines 12 and 14 from which the DC power is produced.
  • the background current generator includes switching transistor 4, shunt resistor 6 and inductor 7 which are connected in series between the line 12 and an anode of a flywheel diode 10 which is to be included in the pulse current generator.
  • the background current generator further includes a reference voltage setting circuit C for producing a reference voltage Ec indicative of a desired voltage to be produced from the shunt resistor 6, a comparator D for comparing the voltage difference between the reference voltage Ec obtained from the reference circuit C and the voltage E6 obtained from the shunt resistor 6 and for producing a signal indicative of the difference, and a background current drive circuit E which, upon receipt of the difference signal, produces a drive signal Ee that controls the on and off states of the transistor 4.
  • the background current drive circuit E forms a chopper circuit together with the transistor 4.
  • a suitable flywheel diode 5 is connected between the line 14 and the emitter of the transistor 4.
  • the comparator D includes an operational amplifier D1, e.g., 741C which is so arranged as to operate according to a so-called hysteresis characteristic wherein an input voltage eA for turning the comparator from inoperative to operative is higher than an input voltage eB for turning the same from operative to inoperative. More particularly, when the voltage difference between the voltage Ec obtained from the reference circuit C and the voltage E6 obtained from the shunt resistor 6, i.e., Ec-E6, reaches, during its increase, a predetermined voltage eA, the comparator D becomes operative to produce a high level signal which is applied to the background current drive circuit E which in turn produces a high level signal Ee to turn the switching transistor 4 on.
  • the comparator D becomes operative to produce a high level signal which is applied to the background current drive circuit E which in turn produces a high level signal Ee to turn the switching transistor 4 on.
  • the current that flows through the transistor 4 then increases exponentially as the inductor 7 accumulates energy. This exponentially increasing current is fedback to the comparator D, and accordingly, the voltage difference Ec-E6 gradually decreases.
  • the comparator D is turned from operative to inoperative to produce a low level signal. Accordingly, the background current drive circuit E produces a low level signal for turning the transistor off.
  • the energy accumulated in the inductor 7 is dissipated through the flywheel diode 5, and accordingly, the current flowing through the shunt resistor 6 decreases. Then, the voltage Ec-E6 increases and when it reaches the predetermined voltage eA, the comparator D operates to turn the transistor 4 on.
  • a DC voltage source C2 is provided for applying a reverse bias voltage to a transistor to speed up the on and off response of the transistor.
  • a contactor C4 is provided for controlling the on and off of the background current generator such that when the contactor C4 closes, the comparator D is turned off to maintain the background current generator in off state.
  • the frequency of on and off should be between several 100 Hz and several 10 KHz.
  • the background current generator described above is a chopper type in which the switching transistor 4 chops the current.
  • chopper type it is possible to employ any other type, such as a thyristor type or a resistor type, so long as the background current generator supplies a stable constant current.
  • the pulse current generator includes a plurality of transistors 8-1,8-2, ... and 8-x which are respectively coupled with resistors 9-1, 9-2,... and 9-x provided for balancing the current flowing through the corresponding transistors.
  • These transistors 8-1 to 8-x coupled with resistors are connected parallel to each other and are inserted in the line 12 so that collectors of the transistors 8-1 to 8-x are connected to a junction 12a and emitters of the same are connected through the respective resistors to a junction 12b which is in turn connected through an inductor 16 to a welding current detector A.
  • the bases of the transistors 8-1 to 8-x are connected through a line 18a to a pulse current drive circuit F and the junction 12b is connected through a line 18b to the pulse current drive circuit F.
  • the pulse current drive circuit F produces a train of pulses Ef between the lines 18a and 18b.
  • the pulse current generator further includes a comparator H which compares a signal Ea indicative of the welding current obtained from the welding current detector A and a reference signal Eg obtained from a reference signal setting circuit G.
  • a difference signal Eg-Ea produced from the comparator H is applied to an AND circuit J which is coupled with a pulse current drive circuit F preferably through an optoisolator.
  • the pulse current generator also employs the chopper method for controlling the pulse current.
  • the pulse current drive circuit F which includes a photo-transistor F1 arranged to receive light signal emitted from the AND circuit J and a contactor F2 which controls the on and off of the pulse current such that when the contactor F2 is closed, the pulse current generator produces no pulse current.
  • the pulse current drive circuit F also includes transistors which are arranged in a similar manner to those provided in the background current drive circuit E.
  • the welding current detector A includes a Hall element A2 which is located adjacent to the line 12 extending between the inductor 16 and a consumable electrode 20 for detecting the electromagnetic effect produced from the line 12 and thus detecting the welding current level flowing through the line 12.
  • a resistor A1 is provided for supplying a constant current to the Hall element A2.
  • a voltage signal produced across the Hall element A2 is amplified by an amplifier A3 which accordingly produces a voltage signal Ea indicative of the welding current flowing through the line 12.
  • the reference setting circuit G and the comparator H are arranged in a manner similar to the reference setting circuit C and comparator D described above.
  • An amplifier H1 provided in the comparator H produces a voltage signal Eh which is indicative of voltage difference between the voltage Ea obtained from the welding current detector A and voltage Eg obtained from the reference setting circuit G, i.e. Eg-Ea.
  • Eh-Ea voltage signal obtained from the pulse frequency control described later
  • the consumable electrode feeding control includes a motor M which is provided in association with a feed roller that feeds the consumable electrode 20.
  • the motor M is controlled by a feed motor control L which includes, as shown in Fig. 10, a thyristor L1, a unijunction transistor L5, capacitor L4, transistor L3 for controlling the current charging the capacitor L4, and amplifier L2.
  • the amplifier L2 produces a signal indicative of voltage difference between a voltage Em which is being supplied to the motor M and a voltage Ek obtained from a reference setting circuit K, i.e., Ek-Em. Such a voltage difference Ek-Em is applied to the transistor L3 so as to control the current flow through the transistor L3.
  • the unijunction transistor L5 produces a train of pulses with a phase relative to the above described voltage difference Ek-Em.
  • the pulses produced from the unijunction transistor L5 is used for triggering the thyristor L1 for controlling the power to be supplied to the motor M.
  • the speed of the motor M is determined by the reference voltage Ek produced from the reference voltage producing circuit K. In other words, so long as the reference voltage Ek is maintained constant, the motor speed is maintained constant.
  • the pulse frequency control includes a welding voltage detector B for producing a voltage signal Eb indicative of voltage across the arc (since the voltage across the arc is relative to the arc length, the voltage signal Eb can be considered as being indicative of the arc length), a reference setting circuit N for producing a reference voltage En, a comparator P for comparing the welding voltage signal Eb with the reference voltage En, an oscillator S and a timer circuit T.
  • a welding voltage detector B for producing a voltage signal Eb indicative of voltage across the arc (since the voltage across the arc is relative to the arc length, the voltage signal Eb can be considered as being indicative of the arc length)
  • a reference setting circuit N for producing a reference voltage En
  • a comparator P for comparing the welding voltage signal Eb with the reference voltage En
  • an oscillator S and a timer circuit T.
  • the reference setting circuit N and the comparator P have the structure similar to those circuits C and D described above in connection with Fig. 7.
  • the reference voltage En produced from the reference setting circuit N is compared with the welding voltage signal Eb in the comparator P, and the difference therebetween En-Eb is amplified, and in turn, applied to the oscillator S including transistor S4, capacitor S1, unijunction transistor S3 and transistor S2.
  • the transistor S4 produces a current relative to the voltage difference En-Eb obtained from the comparator P, and the capacitor S1 is charged by the current determined by the transistor S4.
  • the unijunction transistor S3 When the charged voltage in the capacitor S1 reaches a predetermined level, the unijunction transistor S3 is actuated to discharge the capacitor S1, and at the same time, produces a pulse to the transistor S2. Accordingly, the signal produced from the capacitor S1 has a sawtooth waveform as shown in the first row of Fig. 12, and the signal produced from the unijunction transistor S3 has a rectangular pulse waveform as shown in the second row of Fig. 12.
  • the pulse signal produced from the unijunction transistor S3 is applied to the timer circuit T which includes a counter T1, e.g., pA 555.
  • the timer circuit T produces a train of pulses Et, as shown in Fig.
  • a switch T2 provided in the timer circuit T is provided for setting a desired pulse duration determined relatively to the diameter of the consumable electrode 20.
  • the AND circuit J includes an AND gate J1 and a light emitting diode J2.
  • the pulse produced from the AND gate J1, as shown in Fig. 12, is changed to light signal by the light emitting diode J2 for actuating the pulse current drive circuit F. Accordingly, the welding current applied to the consumable electrode 20 will be as shown by waveform in the last row of Fig. 12.
  • the welding voltage detector B includes a detecting period control circuit U, and a resistor B5 and a diode B4 connected in series between the consumable electrode 20 and workpiece.
  • the diode -B4 is connected in parallel with a coil B2 wound on a core B1. Accordingly, the core B1 formed in a shape of "C" generates a magnetic field which is in relation to the welding voltage.
  • a Hall element B3 is provided adjacent to the core B1 to detect the generated magnetic field and an amplifier B6 is coupled to the Hall element B3 for producing a voltage signal Eb indicative of the welding voltage.
  • the detecting period control circuit U includes a transistor U1 inserted between the diode B4 and the workiece, a photo-transistor U2 connected between the base of the transistor U1 and the workpiece, a light emitting diode U3 coupled to the photo-transistor U2, a switch U4 which selectively connects the cathode of the light emitting diode U3 to one of terminals Ua, Ub and Uc, and an inverter U5 connected between the timer circuit T and the terminal Ua.
  • the terminal Ub is directly connected to the timer circuit T, and the terminal Uc is connected to a DC source.
  • the switch U4 When the switch U4 is connected to the terminal Ua as shown, the pulse produced from the timer circuit T is inverted so that high level signal is produced from the inverter U5 when no pulse is present. Such a high level signal generates the light emitting diode U3 to emit light, and accordingly, the light receiving transistor U2 conducts so as to conduct the transistor U1. Accordingly, when the switch U4 is turned to the position as shown, the detecting period control circuit U detects the period during the absence of pulse, thus the welding voltage detector B detects the background voltage Vb. On the other hand, when the switch U4 is connected to the terminal Ub, the welding voltage detector B detects the pulse voltage Vp, and when the switch U4 is connected to the terminal Uc, the welding voltage detector B detects the average voltage Va.
  • the pulse arc welding device controls the arc length to the predetermined length by the control of the frequency of the pulse current.
  • a pulse arc welding device according to the second embodiment of the present invention.
  • the welding device of the second embodiment is different from the first embodiment in the following points. Firstly, the reference setting circuit C which has been described as connected to the comparator D is eliminated. Secondly, the output of the comparator P which has been described as connected to the oscillator S is connected to the input of the comparator D. And, thirdly, instead of the comparator P, the oscillator S receives input signal from the reference setting circuit K.
  • the welding power control is formed by a background current control which includes welding voltage detector B, reference circuit N and comparator P.
  • the second embodiment is different from the first embodiment in the interconnection between the circuits and since each of the circuits A to T excluding C, Q and R used in the second embodiment are fundamentally identical with those used in the first embodiment, a detail description therefor is omitted for the sake of brevity.
  • the welding device of the second embodiment is so arranged as to control the arc length constant by the control of the background current.
  • the frequency of the pulse current is maintained constant since the oscillator S receives constant voltage from the reference setting circuit K.
  • the third embodiment has the welding power control formed by a pulse duration control which includes the welding voltage detector B, reference circuit N and comparator P which are already described above.
  • the pulse duration control further includes a frequency setting circuit Q coupled with the reference circuit K for producing a train of pulses determined by the reference voltage Ek obtained from the reference circuit K and a pulse duration setting circuit R which determines the pulse duration by the signal obtained from the comparator P.
  • the detail of the pulse duration control is described below.
  • the frequency setting circuit Q includes a transistor Q4, and resistors Q7 and Q8 which are connected in series between a power supplying line and a grounded line.
  • the frequency setting circuit Q further includes transistor Q3, capacitor Q5, unijunction transistor Q2 and transistor Q6 which are connected in a similar manner to those provided in the oscillator S described above.
  • the predetermined voltage produced from the collector of the transistor Q4 is applied to the base of the transistor Q3 so that the capacitor Q5 is charged with a predetermined current.
  • a switch Q1 is provided for selecting the desired current to be supplied to the capacitor Q5.
  • the unijunction transistor Q2 When the voltage charged across the capacitor Q5 reaches a predetermined level, the unijunction transistor Q2 is actuated to discharge the capacitor Q5, and at the same time, a pulse is applied to the base of the transistor Q6. Accordingly, the waveform of the voltage produced across the capacitor Q5 has a sawtooth waveform as shown in the first row of Fig. 17, and the waveform of the pulse Eq produced from the transistor Q16 is as shown in the second row of Fig. 17. Accordingly, the train of pulses Eq produced from the frequency setting circuit Q has a predetermined frequency determined by the reference voltage Ek, which is also used for determining the feeding speed of the consumable electrode 20.
  • the train of pulses produced from the frequency setting circuit Q is applied to a set terminal of a flip-flop circuit R5 provided in the pulse duration setting circuit R which includes a base grounded transistor R6 for amplifying the difference voltage En-Eb obtained from the comparator P.
  • the pulse duration setting circuit R further includes transistor R1, capacitor R2, unijunction transistor R3 and transistor R4 which are connected in a similar manner to those described above in the oscillator S or in the frequency setting circuit Q. Accordingly, the transistor R4 produces a train of pulses in which the duration is varied relatively to the change in the difference voltage En-Eb.
  • the capacitor R2 Since the emitter of the unijunction transistor R3 is connected through a suitable diode R7 to the collector of the transistor Q6, the capacitor R2 is forcibly discharged through the transistor Q6 when a pulse is produced from the unijunction transistor Q2. Therefore, the voltage produced across the capacitor R2 has a waveform as shown in the third row of Fig. 17, and the voltage produced from the collector of the transistor R4 has a waveform as shown in the fourth row of Fig. 17.
  • the pulse signal produced from the collector of the transistor R4 is applied to the clear terminal of the flip-flop circuit R5 so that the flip-flop circuit R5 produces from its terminal Q a duration controlled pulse Er as shown in Fig. 17.
  • a pulse Eq produced from the frequency setting circuit Q sets the flip-flop R5 to determine the step up of the pulse Er and, at the same time, discharges the capacitor R2 to start the charging of the capacitor R2 from the very beginning by the current determined by the voltage difference En-Eb. Thereafter, when the capacitor R2 is charged to a predetermined level, the unijunction transistor R3 is actuated to produce a pulse from the transistor R4 that resets, or clears, the flip-flop, and accordingly, the pulse Er is stepped down.
  • the pulse duration of the pulse Er is determined by the current that charges the capacitor R2, which is in turn determined by the voltage difference En-Eb.
  • the train of pulses Er produced from the pulse duration setting circuit R is applied through the AND circuit J so that the AND circuit J produces a train of pulses as shown in Fig. 17 and thus, the duration of the welding current is controlled.
  • the voltage Eb produced from the welding voltage detector B increases, and accordingly, the voltage En-Eb produced from the comparator P decreases.
  • the voltage impressed on the base of the transistor R1 becomes low to increase the current that charges the capacitor R2. Accordingly, the pulse duration of the pulse Er is decreased so as to decrease the welding current average value la.
  • the terminals Ub and inverter U5 are connected to the pulse duration setting circuit R.
  • the consumable electrode feeding speed is approximately in proportional to the welding current, and the welding current is in proportional to the appropriate arc voltage, it is known that the feeding speed is approximately in proportional to appropriate arc voltage.
  • reference circuit K for setting not only the feeding speed but also for setting the reference voltage for the desired welding voltage, in place of the reference circuit N.

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Claims (18)

1. Verfahren zum Schweißen eines Werkstückes mittels eines Lichtbogens, der zwischen einem Werkstück und einer Verbrauchselektrode erzeugt wird, welche mit konstanter Geschwindigkeit dem Werkstück zugeführt wird, wobei der Lichtbogen durch einen einem Hintergrundstrom überlagerten Impulsstrom erzeugt wird, mit den Verfahrensschritten:
Erzeugung eines Hintergrundstroms mit Konstantstromcharakteristik;
Erzeugen eines Impulsstromes mit Konstantstromcharakteristik;
Steuerung des Impulsstrompegels auf einen vorbestimmten Pegel;
Überlagerung des Impulsstroms über einen Hintergrundstrom;
Abtasten der Schweißspannung, die zwischen der Verbrauchselektrode und dem Werkstück gemessen wird, zum Erzeugen eines Schmelzspannungssignals;
Erzeugen eines Bezugssignals, welches die gewünschte Schmelzspannung anzeigt;
Vergleichen des Schmelzspannungssignals mit dem Bezugssignal zur Erzeugen eines Differenzsignals, welches die Differenz dazwischen anzeigt; und
Steuerung des Mittelwertes des Schmelzstromes durch das Differenzsignal, so daß der Mittelwert des Schmelzstromes in Abhängigkeit von einem Anwachsen des Schmelzspannungssignals über einen vorbestimmten Pegel ebgesenkt wird, und daß der Mittelwert des Schmelzstromes in Abhängigkeit von einem Abfallen des Schmelzspannungssignals unter den vorbestimmten Pegel erhöht wird, wodurch die Schmelzspannung, die von der Bogenlänge abhängt, konstant gehalten wird.
2. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Steuerverfahrensschritt der Hintergrundstrompegel gesteuert wird.
3. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Steuerverfahrensschritt die Frequenz des Impulsstromes gesteuert wird.
4. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Steuerverfahrensschritt die Impulsdauer des Impulsstromes gesteuert wird.
5. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Abtastverfahrensschritt die Schmelzspannung abgetastet wird, die erhalten wird durch einen Durchschnittsstrom zwischen Hintergrundstrom und Impulsstrom.
6. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Abtastverfahrensschritt die Schmelzspannung abgetastet wird, die erhalten wird durch einen Durchschnittsstrom nur des Hintergrundstromes.
7. Verfahren nach Anspruch 1, dadurch gekennzeichnet, daß im Abtastverfahrensschritt die Schmelzspannung abgetastet wird, die erhalten wird durch einen Durchschnittsstrom nur des Impulsstromes.
8. Vorrichtung zum Schweißen eines Werkstückes mittels eines Lichtbogens, der zwischen einem Werkstück und einer Verbrauchselektrode erzeugt wird, welche mit konstanter Geschwindigkeit dem Werkstück zugeführt wird, wobei der Lichtbogen durch einen einem Hintergrundstrom überlagerten Impulsstrom erzeugt wird, gekennzeichnet, durch:
Eine Vorrichtung zum Erzeugen eines Hintergrundstromes mit Konstantstromcharakteristik;
eine Vorrichtung zum Erzeugen eines Impulsstromes mit Konstantstromcharakteristik;
eine Vorrichtung zum Steuern des Impulsstrompegels auf einen vorbestimmten Pegel;
eine Vorrichtung zum Überlagern des Impulsstromes über den Hintergrundstrom;
eine Vorrichtung zum Abtasten der Schmelzspannung, die zwischen der Verbrauchselektrode und dem Werkstück gemessen wird, zum Erzeugen eines Schmelzspannungssignals;
eine erste Bezugserzeugungsvorrichtung zum Erzeugen eines ersten Bezugssignales, welches die gewünschte Schmelzspannung anzeigt;
eine erste Vergleichsvorrichtung zum Vergleichen des Schmelzspannungssignales mit dem ersten Bezugssignal zum Erzeugen eines ersten Differenzsignales, welches die Differenz dazwischen anzeigt; und
eine Vorrichtung zum Steuern des Mittelwertes des Schmelzstromes durch das erste Differenzsignal, so daß der Mittelwert des Schmelzstromes in Abhängigkeit von einem Anwachsen des Schmelzspannungssignals über einen vorbestimmten Pegel abgesenkt wird, und daß der Mittelwert des Schmelzstromes in Abhängigkeit von einem Abfallen des Schmelzspannungssignals unter den vorbestimmten Pegel erhöht wird, wodurch die Schmelzspannung, die von der Bogenlänge abhängt, konstant gehalten wird.
9. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, daß die Steuervorrichtung mit der Hintergrundstromerzeugungsvorrichtung gekoppelt ist, um den Hintergrundstrom zu steuern.
10. Vorrichtung nach Anspruch 9, dadurch gekennzeichnet, daß die Hintergrundstromerzeugungsvorrichtung aufweist:
Eine Vorrichtung zum Treiben des Hintergrundstromes;
eine Vorrichtung zum Abtasten des Hintergrundstrompegels;
eine zweite Vergleichsvorrichtung zum Vergleichen des abgetasteten Hintergrundstrompegels mit dem ersten Differenzsignal und zum Erzeugen eines zweiten Differenzsignales, welches an die Hintergrundstromtreibervorrichtung angelegt wird, zum Erhöhen bzw - Absenken des Hintergrundstrompegels, wenn die Schmelzspannung abfällt bzw. ansteigt bezüglich des vorbestimmten Pegels.
11. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, daß die Steuervorrichtung mit der Impulsstromerzeugungsvorrichtung gekoppelt ist zum Steuern des Impulsstromes.
12. Vorrichtung nach Anspruch 11, dadurch gekennzeichnet, daß die Impulsstromerzeugungsvorrichtung aufweist:
Einen ersten Oszillator, der mit der ersten Vergleichsvorrichtung gekoppelt ist zum Erzeugen eines ersten plusierenden Signals mit einer Frequenz, die durch das erste Differenzsignal bestimmt ist;
einen Zeitregler, der mit dem ersten Oszillator verbunden ist zur Erzeugen des ersten pulsierenden Signals mit einer vorbestimmten Impulsdauer; und
eine Vorrichtung, die im Betrieb mit dem Zeitregler zusammenarbeitet zum Treiben des Impulsstromes, wodurch die Frequenz des ersten plusierenden Signales ansteigt bzw. abfällt, wenn die Schmelzspannung abfällt bzw. anwächst bezüglich des vorbestimmten Pegels.
13. Vorrichtung nach Anspruch 11, dadurch gekennzeichnet, daß die Impulsstromerzeugungsvorrichtung aufweist:
Einen zweiten Oszillator zum Erzeugen eines zweiten pulsierenden Signals mit einer vorbestimmten Frequenz;
eine Pulsdauersetzvorrichtung, die mit der ersten Vergleichsvorrichtung verbunden ist zum Setzen der Impulsdauer in Abhängigkeit vom ersten Differenzsignal für das zweite pulsierende Signal; und
eine Vorrichtung, die im Betrieb mit der Impulsdauersetzvorrichtung zusammenwirkt zum Treiben des Impulsstromes, wodurch die Impulsdauer des zweiten pulsierenden Signals ansteigt bzw. abfällt, wenn die Schmelzspannung abfällt bzw. ansteigt.
14. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, daß die Schmelzspannungsabtastvorrichtung eine Vorrichtung aufweist zum Abtasten einer Periode, in der nur der Impulsstrom vorliegt, und eine Vorrichtung zum Abtasten der Schmelzspannung, die durch einen Durchschnitsstrom des Hintergrundstromes erhalten wird.
15. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, daß die Schemelzspannungsabtastvorrichtung eine Vorrichtung aufweist zum Abtasten eine Periode, in der nur der Hintergrundstrom vorliegt, und eine Vorrichtung zum Abtasten der Schmelzspannung, die durch einen Durchschnittsstrom des Impulsstromes erhalten wird.
16. Vorrichtung nach Anspruch 8, dadurch gekennzeichnet, daß die Schmelzspannungsabtastvorrichtung eine Vorrichtung aufweist zum Abtasten der Periode, in der Impulsstrom und Hintergrundstrom vorliegen, und eine Vorrichtung zum Abtasten der Schmelzspannung, die durch einen Durchschnittsstrom von Hintergrundstrom und Impulsstrom erhalten wird.
17. Vorrichtung nachanspruch 8, dadurch gekennzeichnet, daß die Schmelzspannungsabtastvorrichtung eine Vorrichtung aufweist zum Abtasten eines Zeitraumes, in dem nur der Impulsstrom vorliegt, eine Vorrichtung zum Abtasten eines Zeitraumes, in welchem nur der Hintergrundstrom vorliegt, eine Vorrichtung zum Abtasten eines Zeitraumes, wo Impulsstrom und Hintergrundstrom vorliegen, und eine Vorrichtung zum Auswählen eine dieser drei Zeitraumabtastvorrichtungen zum Abtasten der Schmelzspannung, die entweder durch einen Durchschnittsstrom des Hintergrundstromes, einen Durchschnittsstrom des Impulsstromes oder einen Durchschnittsstrom des Hintergrundstromes und Impulsstromes erhalten wird.
EP81103065A 1981-04-23 1981-04-23 Verfahren und Vorrichtung zum Impulslichtbogenschweissen Expired EP0063619B1 (de)

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DE8181103065T DE3173176D1 (en) 1981-04-23 1981-04-23 Pulse arc welding method and device

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DE3200086C3 (de) * 1982-01-05 1994-09-01 Puschner Peter Elektronische Schweißenergiequelle für das Lichtbogenschweißen mit vorgebbarem statischem und dynamischem Verhalten
US4417129A (en) * 1982-12-20 1983-11-22 Creative Pathways, Incorporated Power source for arc welder
GB2136169A (en) * 1983-03-07 1984-09-12 Welding Ind Of Australia Regulating Pulses for Arc Welding
EP0478796B1 (de) * 1990-04-17 1999-03-17 Daihen Corporation Verfahren zum mag-lichtbogenschweissen und schweissapparat
CN113927130B (zh) * 2020-07-13 2023-08-18 南京理工大学 一种超低热输入的高氮钢电弧增材方法

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US3522411A (en) * 1966-11-28 1970-08-04 Gen Dynamics Corp Weld power supply control system
US3781511A (en) * 1972-03-23 1973-12-25 H Rygiol Method of welding employing square wave current pulses and causing the molten metal to resonate
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